From the British patent specification No. 1,034,201 a turning roll assembly of the type described above is known, whose roller holder can be swivelled manually about an axis arranged obliquely in respect of the axis of rotation of the rollers, which makes it possible to exercize control over the direction, but not over the magnitude of the axial forces which arise between the rollers and the rotating workpiece, and thus provides a certain possibility of counteracting an undesirable axial travel of theworkpiece. With a system of such supports it will presumably be possible by successive adjustment of the individual roller sets prior to the start of a welding operation to achieve a setting where the workpiece, at least during a period, can rotate without axial travel or at the most travel at a sufficiently slow speed to be acceptable for the welding work. However, adjustment can be extremely time-consuming, and altered friction behaviour and deformations in the workpiece, which occur in the course of the welding as a consequence of the heating and of welding stresses, may require after-adjustments in the course of which it may be necessary to interrupt the welding. The problems are further intensified in that the elastic deformations, which are caused by forces between the workpiece and the roller sets, may bring about lack of parallelism between the axes of rotation of individual roller sets leading to new axial forces, which in turn alter the deformations and thus increase the instability.
From the British patent specificaton No. 940,261 a turning roll assembly is known, where swivelling of a turning roll to apply a force to the rotating workpiece to counteract its axial movement is produced automatically in response to this movement. Feelers engaging both ends of the workpiece are connected to one turning roller in such a way that the turning roller is swivelled, when the feeler is axially moved by the workpiece. An automatic compensation of the axial movement of the workpiece is hereby obtained. However, the axial loading of the bearings of the turning rollers is out of control and overloading may occur.